Safety control mechanism



Feb. 13, 1951 DORNBQS r AL 2,541,577

SAFETY CONTROL MECHANISM Filed April 1, 1949 fii} fi fl/a llVVE/VTORS RA. DORA/50s J. 0. FEE/V5) ATTOR/Vf) Pleased Feb. 13, 1951 2.541.571 SAFETY con'mor. MECHANISM Robert A. Dornbos, Chicago, and John D. Feeney,

Downers Grove, 111., assignors to Western Electric Company, Incorporated, New York, N. Y a corporation of New York Application April 1, 1949, Serial No. 84,944

3 Claims. 1

it is necessary for the operatorto use both hands to control the two switches. It has been found, however, that most control circuits of this type are designed in such a way that it is possible for the operator to tie or stake one of the control switches in the closed position, thereby giving him control over the machinery by merely depressing or closing one switch. In this case, maximum operator safety is not maintained since he has one free hand which might easily be caught in the machinery during its operating cycle.

It is an object of this invention to provide a two-button manual circuit control wherein it is absolutely necessary that both buttons be depressed and immediately released to initiate an operating cycle of the machinery under control.

In accordance with one embodiment of the invention, a two-button circuit control device is provided for controlling a power press or like machine wherein a cycle of operation of the press is initiated by the energization of a solenoid which retracts an armature type clutch trip. Upon retraction of the clutch trip, the punch press is driven through one cycle of operation through, for example, a well-known type one-revolution clutch. The control circuit includes two manually operated switches which, when closed, energize a normally open relay and a slow-to-operate normally closed relay and the circuit arangement is such that the clutch trip is not actuated unless both switches are released before the slow-to-operate relay has opened its contacts. It will thus be seen that any attempt to tie or stake" down one of the switches will render the circuit inoperative and it will further be observed that when both switches are released properly, the cycle of operation will take place before the operator can move his hands from the switches to the danger area beneath the press.

Other objects and advantages will more fully appear from the following detailed description when read in conjunction with the accompanying drawings wherein:

Fig. 1 is a partial diagrammatic view of a power press using the invention, and

Fig. 2 is a schematic circuit diagram of one embodiment of the invention.

Referring now to Fig. 1, a punch press, indicated generally at I0, is driven by a sourc of power (not shown) through a conventional onerevolution type clutch ll. One cycle of operation of the punch press to is initiated by retraction of an armature type clutch trip 12, which is retractable into a solenoid IS. The solenoid I3 is energized by means of a control circuit, shown in block form at I! (Fig. 1), and shown in detail in Fig. 2. The cycle of operation is initiated by depressing and immediately releasing a pair of manually controlled switches IE, only one of which is shown in Fig. 1.

Referring now to Fig.2, a control circuit, indicated generally at H, comprises two single pole double throw switches I 5 having A and 13 contacts which alternately connect the solenoid l3 and control circuit H to a source of alternating current 16. A relay l1, having normally open contacts l8, l9 and 20, has its operating coil connected in series with the source of current l6 through the B contacts of switches 15 and a slow-to-operate or time delay relay 2|, having normally closed contacts 22 and 23, has its operating coil connected in parallel with the operating coil of relay H. The solenoid l 3, which is to be energized, may be connected in series with the A contacts of switches 15 across the alternating current supply l6, through the contacts 20 of relay IT. The operating'coil of relay I! may be connected across the alternating current source 1'6 through the B contacts of switches l5, and, upon energization, may temporarily lock operated over the contacts l8 of relay H, the contacts 22 of relay 2!, to one Side of the A. C. source and over the contacts 23 of relay 2|, and the contacts i9 of relay IT to the other side of the A. C. source. The operating coil of relay 2| may be connected directly across the source of current It through the B contacts of switches 15.

In the operation of the circuit, assuming that it is desired to initiate afcycle of operation, the switches [5 are simultaneously moved to their B positions. This operation results in immediate energization of the operating coil of relay i1 and the operating coil of relay 2|. The energization of the operating coil of relay l1 causes its contacts l8, l9 and 20 to be closed immediately, thereby completing a locking circuit from one side of the source l8 through contacts 22. contacts i8, operating coil of relay l1, contacts I! and contacts 23, back to the other side of the source IS. The operation of relay l'l also closes contacts 20, which results in the completion of a preparatory circuit to the solenoid I3. However, since the switches l are now in contact with their 13 contacts, no current will flow to the solenoid i3. At this time, the contacts 22 and 23 of relay 2| will not be opened since relay 2| has a definite time delay or slowto-operate characteristic. With all of the contacts of both relays l1 and 2| now closed, the switches II are immediately moved to their A positions, which operation results in energization of the solenoid I! through the closed contacts 20 of relay II.

It is obvious, from the above description, that in order for an operator to initiate a cycle of operation of the machinery to be operated, it is not only necessary that he depress both switches l5, but also that he release both switches I5 almost immediately. Any delay in the release of the switches l5 will result in a failure 01 the circuit to operate since the time delay of relay 2| is made a very small value. Therefore, it will be seen that after the period of the time delay of relay 2| has run, the contacts 22 and 23 of the relay 2| will be opened, thus rendering the looking circuit inoperative; consequently, release at this time of switches I5 to their A positions will result in immediate release of relay I1, thereby immediately breaking the circuit to solenoid l3 at contacts 20.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A device for controlling the current to a load comprising a relay having an operating coil, a source of current, normally open contacts on said relay in series with said load, a delayed action electromagnetic device having an operating coil and having normally closed contacts controlled thereby, other normally open contacts on said relay in series with the operating coil of said relay and in series with and normally closed contacts on said time delay device, and a pair of switches associated with said source of current and simultaneously movable from a load energizing to a relay energizing position to energize said relay and time delay device and movable thereafter to said load energizing position to energize said load when the contacts of said relay are held closed by a current through the contacts of said time delay device.

2. A safety device for controlling current to a load comprising a source of current, a load device, a pair of separately actuable two-position switches each having a contact at each position and means to connect opposite sides of said current source to like contacts at either position. a relay having its operating coil connected across the second position contacts of said switches and having a first set of normally open contacts connected in series with said load device and the first position contacts of said switches, a slow to operate relay having its operating coil connected across the second position contacts of said switches, second and third sets of normally open contacts controlled by said first mentioned relay and connected in series with its operating coil, two sets of normally closed contacts controlled by said slow to operate relay connected in series with said second and third sets of normally open contacts and the operating coil of said first mentioned relay, each set of normally closed contacts being connected to diiierent sides of said source of current, whereby connection of said current source across said second position contacts energizes the operating coils of said relays and eifects immediate closure of all of said normally open contacts and causes said first mentioned relay to be'locked operated for a time equivalent to the time delay characteristics of said slow to operate relay and subsequent simultaneous connection of said first position contacts across said source before operation of said slow to operate relay energizes said load device.

3. A safety device for energizing a load comprising a current source, a pair oi single pole double throw switches having their movable elements connected to opposite sides of said source, a time delay device energizable from said source through simultaneous contact of said movable elements with first like poles of said switches, a relay having its operating coil connected in parallel with said time delay device, a first pair of normally open contacts controlled by said relay, a load device connected in series with said normally open contacts across second like poles of said switches, a locking circuit for said relay including contacts controlled by said relay effective to lock said relay operated upon energization of said relay operating coil, and contacts controlled by said time delay device effective to deenergize said relay after a predetermined short time interval determined by the time delay characteristic of said time delay device, whereby only simultaneous movement of said elements into contact with said second like poles before expiration of said predetermined time interval results in energization of said load device.

ROBERT A. DORNBOS. JOHN D. FEENEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,369,243 Lechler Feb. 13, 1945 

